Gallery: M celebrates its 40th birthday

The first car to greet us in the old pit lane was the genesis for M - the 3.0CSL.

Before Neerpasch and his gang could make 800hp race cars, they needed to jump through some legislative hoops.

To get BMW on the grid, the company needed to make a homologation special E9 that superseded the CS, or Coupe Sport. This 3.0CSL was the result.

If you're not fluent in BMW, you'd assume the letter ‘L' would mean ‘long' - because most other manufacturers use ‘L' to define a longer limo wheelbase. But this time the ‘L' designation meant "leicht", or light. And as Lotus founder Colin Chapman would tell you, lightness is the best way to make things fast. And the CSL's diet was comprehensive. The steel used for the panels was thinner gauge, and the doors, bonnet and boot lid were all formed from aluminium. The window glass was swapped for racing-style Perspex, and most of the trim and soundproofing was simply chucked in the bin.